1. Field of the Invention
This invention relates to a rotary electrical machine connected to a rotary member heated to high temperature, such as a heater roll used for processing fibers, a ventilation fan for ventilating a high-temperature furnace, etc.
2. Description of the Prior Art
One example of a rotary member heated to high temperatures is a heater roll used for processing synthetic fibers. The heater roll is operative to have synthetic fibers wound thereon in several convolutions for transferring them while imparting suitable tension and heat thereto, so as to thereby give a desired thickness to the synthetic fibers.
The heater roll heated to high temperature is directly connected to a rotary shaft of a rotary electrical machine to be driven thereby. In such heater roll apparatus, precautions presently to be described should be taken. First, it is necessary to cool bearing means journaling the rotary shaft of the electrical machine sufficiently to avoid the trouble which would otherwise occur when the heat of the heater roll is transferred to the bearing means through the rotary shaft and heat the bearing means to shorten the grease life. A proposal has been made to use a cooling mechanism which provides a cooling liquid recycling passage around the bearing means as means for avoiding a rise in the temperature of the bearing means and prolonging its grease life. Some disadvantages are associated with such cooling mechanism of the prior art. The cooling mechanism is complex in construction in a portion thereof near the bearing means, requires additional equipment, such as a circulation pump for recycling the cooling liquid, and increases cost. Also, when such cooling mechanism is used, the heater roll is also cooled as cooling of the bearing means is continued, so that the heating efficiency of the heater roll is reduced and the fibrous products are deteriorated in quality. In addition, such heater roll is required to be detached from the rotary shaft of the rotary electrical machine, to carry out inspection and/or repair of the heater roll or a heater used in combination with the heater roll. Thus it is necessary to select material of suitable hardness for the rotary shaft of a rotary electrical machine which is difficult to damage a portion of the rotary shaft which is fitted to the heater roll, so that the heater roll can be reassembled with a high degree of precision at all times. However, if an alloy steel of high hardness, such as chrominum steel, chromium-molybdenum steel, nickel-chrominum steel, etc., is used for this purpose, the heat of the heater roll will be transmitted in increased amounts to the bearing means because such alloy steel for machine structural use generally has high thermal conductivity. Thus when such alloy steel for machine structural use is used for producing a rotary electrical machine, it is necessary to cool the bearing means sufficiently to prolong its grease life and at the same time heat the heater roll sufficiently to enable fiber processing to be performed as desired. Such heater roll apparatus would be very high in operation cost.